de giers



1955 c. A. DE GIERS Re. 24,075

LIQUID GRAVITY AND WEIGHT GAUGE Original Filed Nov. 14, 1949 5 Sheets-Sheet l 64 j 74 64 6 8 66/ 74 65 I I "'47// 7 70 so 62 7e 72 7o INVENTOR. Clarence .de Giers Attorney Oct. 18, 1955 c. A. DE GIERS LIQUID GRAVITY AND WEIGHT GAUGE 5 Sheeis-Sheet 2 Original Filed Nov. 14, 1949 "F l hh" I I I I llv hflr H lJl i l l l l l l l l I -l fi INVENTOR. Clarence Ade Giers BY Attorney 1955 I c. A. o: GIERS Re. 24,075

LIQUID GRAVITY AND WEIGHT GAUGE Original Filed Nov. 14. 1949 5 Shoots-Sheet 3 mmvrm Clarence A. de Giers Attorney vOt. 18, 1955 C. A. DE GIERS LIQUID GRAVITY AND WEIGHT GAUGE Original Filed Nov. 14, 1949 5 Sheets-Sheet 4 234 POWER SUPPLY Oct. 18, 1955.

. A. DE GIERS LIQUID GRAVITY AND WEIGHT GAUGE 5 Sheets-$heet 5 Original Filed Nov. 14, 1949 RATIO METER FREQ.

and

m e .2 mm 1 Te M .11 m m m o c J m u H mm m mm ,x m 6 u h 2 3 PM n @m" a U 7 m @m J f mm M 2 a Attorney Re. 24,075 Reisaued Oct. 1a, 1955 24,015 uourn cnavrrv AND WEIGHT GAUGE W No. 3,691,296, dated October 12, 1954, Serial No. 127,076, November 14, 1949. Application for reissue Apr! 15, 1955, Serial No. 501,759.

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This invention relates to means for measuring and indicating the specific gravity of liquids, and more particularly to apparatus in which the positions of a plurality of floats of difierent bulk specific gravities control the value of a predetermined electrical characteristic of an electrical element, which may be either a resistance or a reactance (either inductive or capacitive), the positions of the floats being responsive to the specific gravity of the liquid under test. In the case of a variable reactance, its value may in turn control the series-resonant frequency of a circuit including said reactance. This invention relates further to means for indicating the weight of liquids, in which said apparatus is used as a specific gravity compensator in connection with conventional volume indicating means.

Such apparatus, when harnessed electrically to conventional volumetric indicating means, is especially useful in jet type aircraft to inform the pilot or other operating personnel of the weight of fuel present. Fuel tank gauges which involve means for temperature compensation, so as to indicate weight of fuel in the tank and hence the amount of available energy, instead of volume, are in production,

and their performance is excellent as long as they are used with fuel having a specific gravity within the range for which the gauges are designed. But, while such gauges can compensate for minor variations in specific gravity, they cannot give true indications of weight when the specific gravity of the fuel used can vary considerably. Most aircraft engines of the jet type will operate on fuels of widely varying specific gravities ranging from No. 1 fuel oil to high test gasoline. Such apparatus forms the subject matter of a copending application, Serial No. 302,298, filed August 2, 1952, which is a division of the present application. v

This invention may also be used to indicate specific gravity only. Such a use is in determining the average specific gravity of liquid in a large storage tank. It is well known that when liquid is stored, the specific gravity of the liquid near the top is different from that near the bottom. By lowering the apparatus into the tank, the

specific gravity near the bottom, near the top and at such intermediate points as may be desired, may be indicated by a pointer, by a series of lights, or otherwise.

Another use as a specific gravity indicator only is in or recording the specific gravity of liquid flowing through a pipe line. The floats and the necessary electric contacts'can be housed in a separate unit and connected to the pipe line so that a portion of the liquid passing through the pipe line will pass slowly through the housing containing the floats. Again the indication can be made by pointer indication, or by a series of lights, or otherwise.

An important feature of the invention is the use of a plurality of floats of predetermined average or bulk specific gravities graduated within the range of thespecific gravities to be encountered, so that each float will sink or float independently of the others, depending upon the United statesPatent Oflice 2 g specific gravity of the liquid in which the floats are immersed, said floats being harnessed electricallyto provide a progressivechange in electrical resistance or reactance (either capacitive or inductive) as the specific gravity of the liquidvaries. If a variable reactance is used, it, to-

gether with a fixed reactance of opposite sign, may be connected to form a series-resonant circuit, the resonant frequency of which is thus responsive to the specific gravity of the liquid. The resonant frequency may be determined by conventional means. v

Accordingly, it is an object of the invention to provide accurate and simple apparatus for measuring and/or indicating the specific gravities of liquids.

The above and other objects and advantages will appear more fully hereinafter from consideration of the following, description taken in conjunction, with the accompanying drawings in which:

Fig. I illustrates diagrammatically an arrangement for a variable resistance type specific gravity gauge;

Fig. 2 illustrates diagrammatically another arrangement for a variable resistance type specific gravity gauge;

Figs. [1 and 2] 3 and 4 illustrate an arrangement of a float and its electric contacts in which the electric contacts and leads are isolated from the liquid;

Fig. [3] 5 is a side elevation: partly in section on the line [3-3] 5-5 of Fig. [4] 6'showing an embodiment of a float-controlled magnetically operated switch in a specific gravity compensator which may be used in apparatus for indicating the weight of liquid in a tank;

' gig. [4] 6 is a view on line [4-416-6 of Fig.

Fig. [5] 7 is a side elevation of an installation of the embodiment of the invention shown in Figs- [3 and '4] 5' and 6, showing a second float assembly'behind the first;

Fig. [6] 8 illustrates diagrammatically a device for indicating the weight of liquid in a tank, in which a variable resistance type specific gravity gauge is used as a compensator with a variable inductance type fuel quantity indicator;

Fig. [7] 9 illustrates diagrammatically an arrangement for a variable inductance type specific gravity gauge;

Fig. 10 illustrates diagrammatically another arrangement for a variable inductance type specific gravity gauge;

Fig. [8] 11 illustrates diagrammatically an arrangement for a variable capacitance type specific gravity s s lI-l and Fig. 12 illustrates diagrammatically a device for indicating the weight of liquid in a tank, in which a variable The principle of this invention is best understood by reference to Fig. I, which shows a variable resistance type specific gravity gauge. In Fig. I, there are a number of chambers (four are shown, but there may be any number) 20, in each of which is a float 22 or 22' free to move within its confined limits, that is, from the bottom 24 of its chamber 20 to stops 26 at the top of its chamber 20. The float 22 or 22 is weighted as represented by cross.- hatch section 28, so that the floor 22 or 22' will rise when it is lighter than the liquid (not shown) displaced by the float 22 or 22'. T be two floats 22' shown at the far right are lighter than the liquid displaced and hence have risen against the stop: 26. When the float 22' rises and comes in contact with its stops 26, it closes the electric circuit between its stop: 26; and shorts out a predetermined portion of an electrical resistance 30 that is connected by wires 33 to the hto ps 26." The operation just described is repeated as many times as there are chambers 20, each float being weighted corresponding to a difletent bulk specific gravity so that the specific gravity of the liquid will be less than that of the last float 22 resting on the bottom 24 of its chamber and more than that of the first float 22' which has risen against its..stops 26.

Fig. 2 illustrates a more refined version of the invention as embodied in Fig. l, the apparatus being shown at the bottom of a tank 34 containing liquid 36, the specific gravity of which is to be determined. In Fig. 2 are shown two weighted floats 38 resting on the bottom 40 of the tank 34 and two weighted floats 38' which have risen due to their being lighter than the liquid 36 displaced. Again there may be any number of floats. Each of floats 38 and 38' is carried on an arm 42 pivoted about a point 44 and having on its other end a contact 46. Each contact 46 is part of a switch indicated generally at 84, the other contact being shown at 50.- When a float 38' rises, its arm 42 rotates counter-clockwise until contact 46 touches contact 50, thereby closing the switch. Each switch 48 is connected by wires 52 across a corresponding resistor 54, all the resistors 54 being in series, so that when a switch 48 is closed, the corresponding resistor 54 is shorted out. As in Fig. l, the operation just described is repeated as many times as there are floats 38 and 38', each float 38 or 38' being weighted corresponding to a diflerent specific gravity, so that the specific gravity of the liquid will be less than that of the last float 38 resting on the bottom 40 of the tank 34 and more than that of thefirst float 38' which has risen to close 'its switch 48. Thus, again, the number of resistors 54 not shorted out corresponds to a definite specific gravity of the liquid 36, the greater being the specific gravity of the liquid, the smaller being the efiective value of all the resistors 54. The specific gravity of the liquid can be indicated in the same way as described in connection with Fig. 1.

[The principle of this invention is based upon the use of a number of floats, four being shown in each embodiment illustrated in the drawings, but there may .be any number. Each float is free to move up and down within certain predetermined limits and is intended at all times to be totally immersed in the liquid, the specific gravity of which is to be indicated or measured. Each float is dilferently weighted as represented, for example, by the cross hatched section 28 in Figs. 1 and 2, so that the floats in any set will rise or fall at progressively diflerent liquid specific gravities within the range of specific gravities to be indicated or recorded by the particular installation. When each float rises, it will either positively make or positively break (according to the arrangement of the particular installation) a circuit, which will be arranged as hereinafter noted, to cut in or out a section of electrical impedance. The entire installation, therefore, is arranged to control the value of an electrical impedance in accordance with the specific gravitiy of the liquid in which all the floats collectively are immersed. The circuit including the electreial impedance in question may then be so constructed and arranged that the impedance will control an indicator or other means in proportion to the impedance value thereof, so as to indicate an electrical value which may be graduated in terms of specific gravity or which may be arranged to introduce an electrical value which is a function of the specific gravity of the liquid into someoth'er electric circuit means] IIIndlIIlllandlV.

To adapt the invention, i. e., varying electrical impedance, whether it be resistance or reactance, through the use of a plurality of floats of dilferent bulk specific gravitiea, for use inconnection with fuel in an aircraft's fuel tank, or for use 'in connection with other hazardous liquids, it is advisable to isolate the electrical portions, such ascontacts and wires, from the liquid. Figs. 3 and 4 [l and 2] illustrate apparatus which accomplishes this object. We may refer to Figs. [1 and 21-3 and 4 together, for they show the same apparatus in two different positions. A float 6. of ferromagnetic material is totally immersed in or surrounded by the liquid (not shown), the specific gravity of which is to be determined, andisfreetomovefromthebottom 62tothetop64 of a chamber 65. The float will-be in the former position whenits specific mavity is greater than that of the liquid and in the latter position when its specific gravity is less than that of the liquid. As the float 60 rises, a magnetic coupling between the float and a mag! net 66 causes magnet 66 to rotate counter-clockwise about (as shown) a pivot point 68 on a bracket 78 until a contact 70, carried on an arm 72 attached to magnet 66, touches a contact 74, thus closing a switch formed by contacts and 74. Wires 76 may connect contacts 70 and 74 across a portion of a resistance or a reactance (not shown), thus shorting out said portion when the float 60 has risen against the top 64 of its chamber 65, i. e., when the float 60 is of a specific gravity less than that of the liquid. It is to be understood that magnet 66, arm 72, bracket 78, pivot point 68, contacts 7. and 74 and the wires 76 are housed in a sealed chamber 80, and are thus completely isolated from the liquid. With a pluralitycf installations as shown in Figs. [1 and 2] 3 and 4, but with floats of different bulk specific gravities, the desired effect will be obtained as explained generally above.

[lIIandIVIIVandVI Figs. [3 and 4] 5 and 6, both partly in section, are a side elevation and a top view, respectively, of a floatcontrolled, magnetically operated switch, for use in a specific gravity gauge of the variable resistance or reactance type. I

It is to be understood that the float assembly shown in Figs. [3 and 4] 5 and 6 is but one of several float assemblies in the actual gauge, the floats being, as before, of diflerent bulk specific gravities graduated within the range of specific gravities to be encountered. Fig. [5] 7 shows one assembly mounted behind another and will be best understood after considering Figs. [3 and 4] Sand 6, in-which a float arm. carries a spherical float 102 on one end, and a bifurcated box-like frame 164 on the other. Frame 164, which is supported on pivots 106, also supports a pair of magnets 108, one being mounted on each end of frame 104. A switch housing, indicated generally at 110, is centrally disposed in frame 104 and is supported on a hollow pedestal 114 which is mounted on a sealed housing 112 which may serve as a base for all the float assemblies. The switch housing comprises'a sealed hollow drum having an annular shell 116 and double end plates 118 and-124 which are soldered together. Plates 118 carry pivots 122 which support a switch rocker arm (to be described), while plates 124 carry the float arm pivots 106 in alignment with pivots 122. All pivots or bearings may be jewels, in order to reduce friction. This is desirable because of the low power available. The jewels may also serve as insulators for the moving parts inside the switch housing 110.

Centrally mounted on the pivot pins 122, inside the switch housing 110, is a switch rocker arm 126, box-like in structure, of electrically conductive material and provided with a pair of iron pole pieces 128, one on each end of the switch rocker arm 126. In vertical crosssection, the iron pole pieces 128 resemble circular arcs,

ums I ,thecentersofwhichare'ontheaxisofthefloatarm [pi t 151 6 t e. P P

arrr't 126 with. a pair axis of the float arm pivots 106andthepivotpins122.

Whenthefloat182rises,duetoitsbulkspecificgravity being lam than that of the liquid surrounding it, the float arm 18. rotates counter-clockwise as seen in Fig. [3]

-5. Magnetic coupling between the magnets 188 and the pole pieces 128 causes switch rocker arm 126 likeshown partially dotted, which are connected across part of the electric resistance or reactance (not shown), the value of which is to be responsive to the specific gravity of the liquid. The resistance or reactance may be located in the housing 112. The electrical connections in the case of Figs. [3 and 4] 5 and 6 may be exactly the same as in the embodiments of the invention shown in Figs. [6, 7 or 8] 8, 9 or 11 and hereinafter described.

VI VII Fig. [5] 7 shows how a second float assembly 142,as described in connection with Figs. [3 and 4] 5 and 6 may be mounted behind a first float assembly 140 on the base 144. As many such assemblies may thus be mounted as desired or needed.

[VD VIII One of the important-uses which can be made of the invention is as a specific gravity compensator in a gauge for indicating the weight of a liquid, such as gasoline in a tank. To make such a gauge, the .specific gravity compensator may be inserted in a circuit which would otherwise constitute a gauge for indicating merely the volume of liquid. Fig. [6] 8 shows diagrammatically a circuit including a specific gravity compensator of the variable resistance type which can be used to indicate the weight of the liquid. [The compensator, indicated diagrammatically at 150, is designed to cut in or out sections of a resistance as hereinafter described. The details of the switches, shown diagrammatically by way of example, could be as illustrated in Figs. 1-2 or in Figs 3-5, or as particularly described hereinafter in connection with Fig. 7. The compensator 150 controls the effective resistance value of a group of] The compensator, indicated generally at ISO, is similar to that illustrated in Fig. 2, although it could just as well be any one of the variations. The compensator 150 controls in the manner described, the efiecrive value of a group of resistors 152, 154, 156 and 158, only four being shown.

6 the secondary 172 and a point 188 162 and the reference coil 168, andis fed to an outputtransformer 182. The secondary 184 of the transformer 182- is shunted by the resistors 152, 154, 156 and 158, and by another resistor 186 of the specific gravity r 150. While shunt-connections of the resistors have been shown, series connections. or potentiometer maybeused. Ameasuringcircuit188isconnectedacross the secondary 184 of the output transformer 182 and will detect the output of the bridge circuit, and may compare it with a reference signal from an indicator 1!. by a feedback connection 192. The signal may be amplified by an amplifier 194 and be made to control the indicator 190. This, in efiect, is a servo type circuit.

-Inoperation,thebridgewillbearrangedtobein balance (that is, no output) when there is no lquid in the tank. Under this condition, all the floats of the compensator will be down, a condition which would correspond to having the tank full of very light liquid. However, since the output is zero, there will be no error in the reading of the indicator 186. As the tank is filled, the bridge will become more and more unbalanced due to change in the inductance of the coil 162, and the output of the bridge to the measuring circuit 188 will become progressively greater. If the specific gravity of the liquid now changes, the compensator 150 will further modify the output of the bridge by cutting out resistors or by adding them to the circuit depending on the direction of the variation. Thus, the final reading of the indicator will be a truer indication of the contents of the tank by weight than if the compensator 150 were It should be understood that the volume-responsive element 160 could just as well be capacitive, in which case the reference coil 168 would be replaced by a reference capacitance.

m IX The invention, as embodied in a variable reactance type specific gravity gauge, may be understood by referring to Fig. [7] 9, inwhich any numberof float assemblies collectively indicated at 210 (only four are shown) are .near the bottom of a tank 212 containing liquid 214, the

specific gravity of which is to be determined. [It will be understood that each float operated switch could, for example, take the form of Figs. l-2 or of Figs. 3-5. As illustrated, however, each] Each float assembly comprises afloat 216 or 216' carried on one end of an arm 218 pivoted at a point 220. Each float 216 is shown at the The fuel volume measuring element, indicated general- 1y at 160, is a variable inductance coil 162, which is responsive to the liquid level by means of afloat 164 connected to a permeable core 166 arranged to move into or out of the coil 162 as the float'164 risesor falls in response to changes .in liquid level, the liquid not being shown. This movement changes the inductance of the coil 162. It is to be noted that the liquid level responsive device, here the coil 162, in itself compensates for minor changes in specific gravity, but is ineffective when the specific gravity varies widely, as. it mayfrom time to time in the case of fuel in the tanks of jet type aircraft. The

coil 162 is an element of a bridge circuit which includes,

in addition to'coil 162, a reference coil 168, and the I secondary 172 of a transformer 170 which may be energized by an audio frequency power supply 176 connected lower end of its arc, while each float 216' is shown at the upperendofitsarc. 0ntheotherendofeacharm2l8 is an electric contact 222, which is part of a switch indicated generally at 224, the other contact being shown at 226. When a float 216 travels upwardly along its arc, due to its bulk specific gravity being less titan that of liquid 214, its arm 218 rotates counterclockwise (as seen in Fig. [7] 9 until contact 222 touches contact 226, thereby closing switch 224. Each switch 224 is connected across a respectively corresponding predetermined portion 225 of an inductance 228, so that when a switch 224 is closed, its corresponding predetermined portion 225 of inductance 228 is shorted out. Coil 228 is shown as a single coil tapped at various sections, but it will be understood that a number of separate coils may be used. The operation just described may be repeated as many times as there are floats 216 and 216', each float 216 or 216' being weighted corresponding toa diflerent bulk specific gravity, so that the specific gravity of the liquid 214 will be less than that of the last float 216 at the lower end of its arc and greater than that of the first float 216' at the upper end of its arc. Thus, the amount of the inductance 228 not shorted out corresponds to a definite specific gravity of the liquid 214, the greater being the specific gravity of the liquid, the smaller being the eflective value of the inductance 228. Coil 228 is connected in series witha condenser 23., which together form a series-resonantcircuit, the resonant frequency of which is a definitefunction of the value of the inductance 228, and is given by the formula 1 Mm where f is the resonant frequency in cycles per second, L is the inductance of the coil 228 in henrys, and C is the capacity of the condenser 230 in farads.. The resonant frequency of'the circuit including coil 228 and condenser 230 controls the frequency of oscillation of a variable frequency oscillator 232, shown in block form, whichmay be so constructed that it will oscillate at. said resonant frequency, as is well known in the art. The oscillator 232 is energized by a power supply 234. The frequency of oscillation of oscillator 232 may be measured by any convenient form of frequency meter, shown in block form at 236, which may be calibrated to indicate specific gravity directly.

In operation, the specific gravity-sensitive floats 216 and 216' may be placed in tank 212 for the purpose of determining the specific gravity of the liquid 214 therein. If it be assumed that the liquid 214 is of an average specific gravity, the system can be adjusted so that, for example, halfthe floats 216 are at the bottoms of their arcs and the other half are at the tops of their arcs. This means that half the switehes224 will be open and the other half will be closed. Thus some of the turns of coil 228 will be shorted out, causing the oscillator 232 to genance, thereby causing the oscillator 232 to generate asignal of greater frequency. Thefrequency meter 236 can then be conveniently cahbrated to indicate specific gravity directly.

The apparatus shown in Fig. is in most particulars identical with that of Fig. 9. The only exception lies in the method of changing the inductance of the inductive element of the series resonant circuit. In the case of Fig. 10, any number of separate coiLs 240 (only four are shown) are used, each placed near the top of a chamber 242 containing a float 244 or 244' free to move from the bottom to the top of its chamber 242. Chambers 242 are near the bottom 246 of a tank 248 containing liquid 250, the specific gravity of which is to be determined. The floats 244 and 244' have bulk specific gravities graduated within the range of specific gravities to be encountered, as explained in the description of Fig. 9. Each float 244 or 244' is adjusted so that, responsive to the specific gravity of liquid 250, it will approach or recede from its respective coil 240 As a float 244' rises in the liquid 250 surrounding it, it approaches its corresponding coil 240, increasing the inductance thereof, the floats 244 and 244' being of ferromagnetic material. As before, the rest of the circuit comprises a condenser 252 in series with coils 240', an oscillator 254 connected also to a power supply 256 and a frequency meter 258 which may be conveniently calibrated to read specific gravity directly.

For operation, again the system can be adjusted so that for liquid of average specific gravity, half the floats, i. e. floats 244 will be down (of bulk specific gravity greater than that of the liquid) and half the floats, i. e. floats 244' will be up (of bulk specific gravity less than that of the liquid), resulting in a mid-scale reading of the frequency meter 258. If liquid of greater than average specific gravity is substituted, one of the floats 244 will rise, thus coming closer to its corresponding call 240 and increasing itslnductance. This decreases the frequency generated by the oscillator 254 again in accordance 'with the 'formula On the other; hand, iflighter than average liquid is substituted, the opposite rJect will occur, that is, one of the floats 244' will sink, thus receding from its corresponding coil 250, and the eflective inductance of the coils 240 will decrease correspondingly. This increases the frequency of the signal generated by the oscillator 254.

[VIII] XI tains a series-resonant circuit including inductive and,

capacitive elements. However, in this case, instead of varying the inductive element responsive to changes in the specific gravity of the liquid under test, as done in the [circuit of Fig. 7] circuits of Figs. 9 and 10 the capacity is changed. The arrangement of the floats shown in Fig. [8] II at 260 and 260' and their corresponding switches, shown generally and diagrammatically in Fig. [8] II at 262, is exactly the same as in the apparatus shown in Fig. [7] 9 and need not be described again. Again, the float assembly is illustrated near the bottom 264 of a tank 266 containing the liquid 268 under test. The series-resonant circuit in the case of Fig. [8] 11 starts with a lead wire 270 from a variable frequency oscillator 272, and comprises a fixed inductance 274 in series with a condenser 276, which is connected by a lead 271 back into the oscillator 272. The oscillator 272 again is energized by a power supply 278, but as a variation from the circuits described in connection with [Fig 7] Figs: 9 and 10, the oscillator 272 is arranged to feed into a frequency discriminator 280 from which suitable currents may be derived to operate a ratiometer 282 and a pointer (not shown).

One side of each switch 262 is connected to the lead 271 and a condenser 284 is connected in series with the other side of each switch 262 respectively. The side of each condenser 284 remote fro'm'its corresponding switch 262 is connected to the end of the coil 274 remote from the oscillator 272. Thus when a float 260 is at the top of its arc, due to its specific gravity being less than that of the liquid 268, its corresponding switch 262 is closed.

' With the switch in this condition, the corresponding condenser 284 will be connected in parallel with the condenser 276.

In operation,'the apparatus may be adjusted so that for a liquid of average specific gravity, half the floats, i. e. the floats 260 will be at the bottoms of their arcs and half the floats, i. e. the floats 260 will be at the tops of their area. If a liquid of greater than average specific gravity is substituted, one'of the floats 260 will rise, thus closing its switch 262, and connecting its corresponding condenser 284 in parallel with the condenser 276. Thereby, the overall capacity of the series-resonant circuit including the coil 274 and the condenser 276 is increased, since when two condensers are connected in parallel, the equivalent series capacitance is the sum of the capacitances of the two condensers. Conversely, if a liquid of less than average specific gravity is substituted, one of the floats 260' will sink, thus opening its switch 262 and decreasing the capacitance of the series-resonant circuit by the value of its corresponding condenser. As

' is the case in the circuits shown in [Fig. 7] Figs. 9 and 10, these changes in the specific gravity of the liquid under test are reflected in changes in the frequency of the signal generated by the oscillator 272. When the capacitance increases (due to an increase in specific gravity), the generated frequency decreases, and vice versa. These trequeucychangcsareinturnrcflectedbychangcsintheindicator readings, as in the other circuits.

As is the case with a variable resistance type gauge, one

of the important uses which can be made of a variable reactance type specific gravity gauge is as a specific gravity compensator in a gauge for indicating the weight of a liquid, such as gasoline, in a tank. To make such a gauge, the specific gravity compensator may be inserted in a circuit which would otherwise constitute a gauge for indicating merely the volumepgi liquid present. Fig. 12 shows diagrammatically a including a specific gravity compensator whichc'an be used to indicate the weight of a liquid 290 in a tank 292. In Fig. 12, the compensator, is indicated generally at 296, and is similar to that illustrated in Figs. 2 and 10, .exceptthat as a matter of conven'ience, the unit is turned upside down. The compensator 296, which, in the manner described, controls the inductance of a group of coils 298, could just as well be of the variable capacitance type, as shown in Fig".

The fuel volume responsive element is a condenser, formed of inner and outer spaced concentrically-positioned metal cylinders 302 and 304, 'which are supported vertically in the tank 292 by insulating supports, as at 306, which may be formed of any suitable insulating material. The cylinders 302 and 304 extend substantially from the bottom to the top of the tank 292, so that the capacitance of the condenser 300 is a function of the depth of liquid in the tank 292. The depth of liquid between the plates 302 and 304 of the condenser 300 is the'same as that in the rest of the tank 292. The capacitance is a function of liquid level because capacitance depends upon the dielectric constant of the insulating medium between the plates of the condenser, gasoline, for example, having a dielectric constant of approximately two, the dielectric constant of air being one. Therefore, when the air between the condenser plates 302 and 304 is replaced by gasoline, the capacity of the condenser increases by a factor of two, with proportional changes taking place when the gasoline only partially fills the space between the condenser plates 302 and 304. r I

A fuel quantity indicator of the variable capacitartce type in itself compensates for minor variations in specific gravity, but is ineffective when the specific gravity varies over a wide range, as it may in the case of fuel for most jet-type aircraft engines. In such a case, the specific gravity compensator will substantially reduce the efiects of such wide variations.

In the apparatus shown in Fig. 12, the circuit may be energized by an audio frequency power supply 308. The output of the power supply 308 is applied to a bridge circuit comprising an input transformer 310, the volume responsive condenser 300, and a reference condenser 312. both of the last-mentioned elements being in series with the output of the transformer 310. The output ofthe bridge circuit is taken from a point 314 on the secondary of the transformer 310 to a second point 316 which is grounded between the condensers 300 and 312. Between points 314 and 316 are the specific gravity compensator 296 and the primary of an output transformer 318 in series. The secondary of the output transformer 318 feeds into a measuring circuit 320 which will detect the output of the bridge circuit andin turn will operate an indicator 322 which may be conveniently calibrated to read, for. example, in pounds of liquid.

For operation, the bridge circuit may be adjusted so that when there is no liquid in the tank, the bridge circuit will be in balance (that is, no output). dition, all the floats of the compensator 296 will be down, a condition corresponding to having the tank 292 filled with liquid of a very low specific gravity. However, since the output is zero, there will be no error in the reading of the indicator 322. As the tank 292 is filled, the bridge Under this conshown near the bottom 294 of the tank 292, 5

will become more and more unbalanced, due to the in crease (already explained) in the capacitance of the condenser 300. The result will be a greater and greater output to the measuring circuit 320. If the specific gravity of the liquid now changes, the inductan'ce of the coils 298 in the compensator 296 will also change, thus modifying the output" to the measuring circuit 320 through the transformer 318 by causing a smaller or greater voltage to be applied thereto, depending upon whether the specific gravity has increased or decreased. 1f the specific gravity has incerased, more floats of the compensator 296 will rise, thus decreasing the inductance of the coils 298.

In this event, a greater voltage will be applied across the v transformer 318, thereby increasing the output to the measuring circuit 320.

Thedescribcd apparatuswillbescentoptbvidea simple, accurate and reliable'mt and indication of the specific gravity ofaliquid inaccordauce with the objectives of the present invention, but it is to be understood that the invention is not limitcdto the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as deflncdhythefollowingclaims.

I claim:

1. Apparatus for measuring the specific gravity of a liquid within a predetermined range, a plurality of floats having respectively diflerent bulk specific gravitics graduated within said range, each of said floats having a substantially predetermined range of movement and being mounted in the liquid, the spcciflc gravity of whichistobcmeasurcd,soastobeadiaccnttothe top or bottomof itsrangc ofmovement respectively as its bulk specific gravity is less or greater than that of the liquid; each of said floats having movable therewith first ferromagnetic material, a plurality of switches, each including contact means and second ferromagnetic material, each of said switches being responsive to the position of one of said floats respectively by means of magnetic coupling between said first and second ferromagnetic material; an electrical impedance having a section controlled respectively by each of said switches, so that each impedance section will be cut in or out depending on the position of the one of said floats respectively associated therewith as aforesaid, whereby the resulting electrical-valucotsaidimpcdanceisapredeterminedfunction at the specific gravity to be measured; and indicating means controlled at least in part by said resulting electrical value of said impedance, so that the indication afforded by said indicating means will be a function of the specific gravity of the liquid being measured.

2. Apparatus according to claim 1, wherein said electrical impedance is a resistor.

3. Apparatus according to claim 1, wherein said electrical impedanceisanelcctrical rcactance means.

4. Apparatus according to'claim 1, wherein each of said floats is secured to one end of a float arm, each said floatarmcarryingabifurcatcdportionspacedfi'omits respective float and two magnets comprising said first feetic material and mounted in spaced relationship within said bifurcated portion, wherein each of said switches is disposed in a liquid-tight housing fixed in position, each said housing being positioned between its respective magnets, each of said switches being responsive to the position of its respective float, each said housing l 1 second contact means mounted on insulating material withinsaidhousingandadaptedtobeengagedbyaaid first contact means.

5. Apparatus according to claim 1, wherein each of sard floats is secured to a float arm, each said float arm carrying said first ferromagnetic material, wherein each of said switches is disposed in a liquid-tight housing, said for each switch being positioned adiacent to sard first ferromagnetic material, said float arm being rotatably mounted on said housing, eachof said switches berng responsive to the position of its respective float, each of said switches including a rocker arm bearing first contact means and having said second ferromagnetic material secured thereto, said rocker arms being positioned in response to the rotative position of said first ferromagnetic material due to magnetic coupling between sard first and- 12 said indicating means comprises an indicator connected in said circuit and responsive to the series-resonant frequency thereof, so that said indicator will indicate a value directly characteristic of the specific gravity of said liquid.

9. Apparatus for indicating a value which is a function of the density of a liquid in a container, in which the density of the liquid is within a predetermined range, comprising a plurality of floats of predetermined difierent bulk densities graduated throughout said range, means loeating each of said floats adjacentto the bottom of said container and constraining each said float to a limited movement up or down according as it is lighter or heavier than the liquid displaced thereby, so that said floats will ,always be completely immersed in said liquid, so that the positions of said floats are independent of any variations in the level of the liquid in said container throughout a range of liquid levels from "full" down to a point adjacent to an "empty" condition of the container and so that said positions are also substantially independent of the attitude of the container throughout a relatively wide range of operating attitudes; an electrical circuit having a plusaid indicator, said circuit including means for measuring the series-resonant frequency of the seriesconnected reactance means aforesaid, and said indicator being controlled by the measured frequency of said circuit, so as to indicate the specific gravity of said liquid.

7. Apparatus according to claim 1, wherein said electrical impedance comprises a variable electrical inductance responsive to changes in the podtions of said floats, and an electrical capacitor connected in series with said inductance to form a series-resonant circuit; and wherein said indicating means comprises an indicator, and means responsive to the series-resonant frequency of said resonant circuit for controlling said indicator to indicate a value which is a function of said frequency and which is directly characteristic of the specific gravity of said liquid.

8. Apparatus according to claim 1, wherein said electrical impedance comprises electrical capacitance means including a plurality of capacitors, current flow through which is controlled by each of said floats respectively, a series-resonant circuit including all said .capacitors in parallel and a series-connected inductance; and wherein rality of increments of impedance corresponding to the number of said floats, each impedance increment being constructed and arranged to be varied by the "up" or "down" positions of said floats respectively, and an indicating means connected to said circuit so as to be controlled at least in part by the total impedance thereof as afiected by the positions of said floats respectively for indicating a value which is a function of the density of the liquid in the container.

10. Apparatus in accordance with claim 9, in which said impedance increments are increments of resistance.

11. Apparatus in accordance with claim 9, in which said impedance increments are increments of inductance.

12. Apparatus in accordance with claim 9, in which said impedance increments are increments of capacitance.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS 1,285,145 Harrington et al Nov. 19, 1918 1,956,984 Dunzweiler et al May 1, 1934 2,053,353 Talbot Sept. 8, 1936 2,233,297 Polin et al. Feb. 25, 1941 FOREIGN PATENTS 539,3s4 Great Britain Sept. 9, 1941 

